A good-quality slit separator having a small amount of fuzziness at a slit part thereof is to be obtained. The present invention includes: a step (S101) of conveying an original sheet (S); and a step (S102) of slitting the original sheet (S) by causing a plurality of slitting blades (72) to cut into the original sheet (S) such that tangent plane angles (63) in a tangent plane, on which a slitting position is in contact with the original sheet (S), are substantially identical with each other.

A good-quality slit separator having a small amount of fuzziness at a slit part thereof is to be obtained. The present invention includes: a step (S101) of conveying an original sheet (S); and a step (S102) of slitting the original sheet (S) by causing a slitting blade (72) to cut into the original sheet (S) such that a d tangent plane angle (.sub.3) in a tangent plane, on which a slitting position is in contact with the original sheet (S), is in a range of not less than 3 to not more than 35.